This invention relates generally to the field of integrated circuits and more particularly to an oscillator and method.
Integrated circuits often employ an oscillator, or clock source, which generates a fundamental frequency. In many cases, it is desirable for the clock source to be internally-generated and contain no external parts, such as resonators, crystals, or capacitors. Typically, in such circuits, reduction of circuit complexity and circuit area is desirable. Changes in design or manufacturing requirements may impose changes to the frequency desired for the oscillator. For example, a subsequent generation of an integrated circuit may operate at a higher speed. Such changes present challenges to traditional oscillator designs, which have typically been addressed by changing the design of the oscillator or with the use of phase-locked loop (PLL) technology, both of which introduce additional design cost and may extend development time. Therefore, an oscillator that can be easily adapted to generate multiples of the original fundamental frequency is needed.
One aspect of the invention is an integrated circuit comprising a fundamental frequency oscillator comprising a reference node whose voltage varies between a high threshold and a low threshold. The fundamental frequency oscillator is operable to generate a first output at the fundamental frequency on a first output node. The integrated circuit also comprises a circuit coupled to the reference node. The circuit is operable to sense the voltage at the reference node, to determine when the voltage exceeds an intermediate threshold between the high threshold and the low threshold, and to generate a second output in response to the determination. The integrated circuit also comprises logic coupled to the circuit and load circuitry coupled to the logic. The logic is operable to generate an output signal at an output frequency greater than the fundamental frequency in response to the second output. and the first output.
The invention provides several important advantages. Various embodiments of the invention may have none, some, or all of these advantages. It allows a higher frequency to be generated with few modifications to an existing oscillator design. The invention may reduce design time, and cost of the design. It also allows the use of existing oscillator designs or other circuitry, such as frequency trimming circuitry. Some embodiments of the invention may be used to generate an integer multiple of the original fundamental frequency of the oscillator. Rather than employing higher bandwidth analog devices (such as comparators) to achieve a higher frequency output, the invention allows generation of higher frequency output using the same devices employed in an existing oscillator design with a fundamental frequency below the higher frequency. This advantage may further reduce design time and cost as well as potentially lowering power consumption. It may achieve these advantages while using relatively little additional integrated circuit area and current drain compared to the existing oscillator design used to generate a higher frequency in accordance with the invention. It also may allow generation of multiple frequencies that can all be used simultaneously in an integrated circuit, without requiring multiple oscillators.